In response to a demand for higher density packaging, multilayered ceramic substrates having conductors interposed therein are now on the verge of practical use. The materials used for such substrates are low-temperature firable substrate materials which can be fired below 1,000.degree. C. so that Ag and similar conductive materials having a low resistance may be fired at the same time. The inventors previously proposed a low-temperature cofirable substrate material having high strength in Japanese Patent Application Kokai No. 132194/1989. Such a low-temperature cofirable substrate is used by printing a resistor 1 and a conductor 2 on a low-temperature cofirable substrate 3 as shown in FIG. 1 whereupon it is covered with an overcoat 4 of inorganic glass material. However, if the low-temperature cofirable substrate 3 is fired after it is covered with the overcoat 4, there arises the problem that cracks 5 can generate due to thermal shocks in the overcoat 4 particularly in proximity to the conductor 2. Cracking entails problems of varying the resistance of the resistor 1 on the substrate and cracking the resistor 1 and causes migration to occur from the conductor 2 printed to the substrate, resulting in a loss of reliability.